#include <iostream>
#include <cstdio>
#include <algorithm>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#define int long long 
using namespace std;
void solve()
{
    int sum = 0;
    int m,k;
    cin >> m >> k;
    for(int i = m; i <= k; i++)  sum += i;
    cout << sum << endl;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0),cout.tie(0);
    int t = 1;
    while(t -- )  solve();
    return 0;
}